Hello!
I have just bought two maple min rev 3. I can not understand the function of the av+ av- and vbat pin. Can someone explain me their purpose? THANKS A LOT
av+ av- e vbat pins function?
(3 posts) (3 voices)-
manitou
MemberCheck out chapter 5 of the reference manual
http://www.st.com/web/en/resource/technical/document/reference_manual/CD00171190.pdf
and the schematic shows a separate voltage regulator supplies the ADC
https://github.com/leaflabs/maplemini/blob/master/maplemini.pdfPosted 1 year ago # -
gbulmer
ModeratorHopefully to make it a bit easier easier:
av+ is a regulated 3.3V supply for analogue circuitry. It is independent from the digital +3.3V supply output, and delivers a lower noise power source. For example, if you were using a resistive sensor in a voltage divider (fixed resistor and resistive sensor in series), then you might use av+ as the high-end voltage because it well have less noise than the 3.3V supply.
av- is the ground return for that analogue supply, so if you were using that resistive sensor/voltage divider, it's low-end voltage would be tied to this.
Remember that the Maple has a 12bit ADC (0 to 4093) measuring between 0V and 3.3V, so a single bit change is less than 1 millivolt (about 6x more sensitive than a 10bit 5V ADC e.g. an Arduino), so noise on the power supply can become very important.
It's problem is that it can only supply limited current when the mini is powered from much above the 5V USB supply. But if your using USB, then you should be able to draw well over 100mA (IIRC). If you aren't aiming for low-noise analogue samples, then you could use it just like a second 3.3V supply (remembering not to drawn too much current from either).
vbat is an input power source fr the STM32 on the maple mini. The maple mini contains a real-time clock which can be maintained by an external battery when power is removed from the mini. It isn't simple to use though, it needs a 32KHz oscilator too, to get it working.
(Full disclosure: I am not a member of LeafLabs staff.)
Posted 1 year ago #
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